Fog inhibitor for photographic emulsions



Patented June 7, 1949 FOG INHIBITOR FOR PHOTOGRAPHIC EMULSIONS William F. Smith and Robert E. Stauffer, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. 1., a corporation of New Jersey No Drawing. Application December 19, 1947,

Serial No. 792,844

a c aims. (01.954)

It is known that photographic emulsions, particularly ultra-sensitive emulsions or those containing optical sensitizers exhibit a tendency to form upon development a deposit of silver in the emulsion. This depositextends more or less uniformly over the entire emulsion and is known as fog. Photographic fog is of two types: local and general. Local fog is formed by exposure of the film or plate at undesired points as by a light leak in the camera. General fog'is formed in a number of ways. It may be caused by the conditions under which the film or plate is stored, such as conditions of high temperature or humidity r unusually longtime of storage. The nature of the emulsion may also produce general jog as well as the conditions of development of the emulsion as by development for protracted periods of time or at temperatures above normal. We are primarily concerned with fog and sensitivity changes produced in films or plates on development after storage under adverse conditions of high temperature and humidity or both.

v General fog and loss of sensitivity of the emul" sion are especially likely to occur when the sensitive material is stored under conditions other than ideal, that is, under conditions of high tem perature and humidity as in tropical regions.

It is an object of the invention to provide novel anti-fogging or fog-inhibiting compounds for emulsions. A further object is to provide antifogging agents which stabilize the initial sensitivity of the emulsion. A still further object is to provide anti-fogging agents which improve the keeping of the emulsion. in tropical regions.

Other objects will appear from thefollowing de-,

2 sage of time under non-ideal conditions of storage.

A solution of palladium nitrate, Pd(NO3)2 when added in suitable concentration before coating to unsensitized or optically sensitized photographic emulsions does not afiect appreciably the sensitometric values for sensitivity and fog when measurements are made soon after coating. When sensitometric measurements are made after appreciable intervals of time under tropical or dry conditions of storage at elevated temperatures, however, this compound does stabilize photographic speed and maintain fog at a low level.

The preparation of silver halide emulsions involves three separate operations, (1) the emulsification and digestion-or ripening of the silver halide, (2) the freeing" of the emulsion from excess soluble salts usually by washing, (3) the second digestion or after-ripening to obtain in creased sensitivity (Mees, The Theory of the Photographic Process, 1942). We prefer to add the fog-inhibiting agents after the final digestion or after-ripening although they maybe added before digestion. The most useful concentration range of fog. inhibitor is from .260 to 3.90 gm. of fog inhibitor per kilogram of silver nitrate used in making the emulsion and converted to silver halide. This amount will vary,

e. g. depending upon the particular silver halide.

used.

The anti-foggant and stabilizing action was determined by incubation of the emulsions under simulated tropical conditions and also by incubation in dry heat at F. for various lengths of time after six days to one month. The results of these aging tests are tabulated here and are compared with the initial speed, gamma and fog'.

of the emulsions with and without the anti-foggant' and stabilizing compound. 'The'tests from which the following tabulation was made used a high-speed orthochr'omatic negative type of emulsion exposed on an Eastman type 'IIB sensitom-' eter and developed for five minutes in a devel op'er of the followingbompositibn'z' Water to one liter.

3 The results compared to other simple palladium salts are as follows:

'4 scribed may be used in various kinds of photographic emulsions. In addition to being useful G t d Original 12 days 120 F.

ms. compoun sifiple t a 't i izs i ii 10/i 10 1 ver e o g emulsion Speed Gamma Fog Speed Gamma Fog 785 1.; .1 1 550 1.39 .20 775 1:21 .10 850 1.54 18 690 11.28 12 .890 1.10 18 710 l. 28 07 690 1. 32 11 210 1. 46 14 110 1. 59 .20 165 1. 70 10 95. 1.59 .34 55 1. 75 32 57. 5 1. 59 27 None 740 127 -.09- 710 -120- "13 PdCiz.2H;O, 1.03.. 400 1538 .10 295 1.50 f I1 PdCh.2H,O, 1.55 275 1. 48 07 155 1 51.132 11 PdCl1.2H1O, 2.06 235 l. 55 .06 140 1. 50 14 18 days 120 F. 4 weeks trop. 8 weeks trop. Sam- 16 li u/i 0. mi 1 speed Gamma Fog speed Gamma Fog speed Bamrna Fog 435 1. 45 26 1 21 230 1. 19 ."56 830 1. 32 24 16 500 1. 20 21 870; 1.29. 2- .21 .425 1.20 .28 955 1308' F09 12 "355 l. 40 .20 110 1.50 .34 b1 ck 1.0 83 1.52 .51 lack, a 1.o 48 1.165 532 16 69:0 1. 60 18 575 1439 :24 .27 '345 1.26 .37 390- 4.35, .16; black black 1 70 134B .14 black black 138 1.52 .18 black blao It willbe noted from-the data that the improve ment in fog using the compound of the invention is appreciable as compared tothe same tests carried out on the emulsion containing palladium sulfate or palladium chloride. Inthi's resp'e'ct,the compound of our invention is unique in that it represents one 'o'f the few'simple 'salts 'of metals of the platinum group which are effective in reducing fog. In theSmith and :Trivelli U. S. applica-' tion Serial No. 792,843, filed concurrently herewith, now Patent .No. 2,472,626, Iissued June 7, 1949, another simple 'salt of the platinum group, ruthenium tri-chloride, 15 described and claimed.

One of the advantages of ourinvention 'is the fact that the compound 'may :be prepared with high purity compared'to organic types of "f'og'inhibitors. Another and perhaps chief advantage is the greater extent of stabilizing action :over *a' wide range of climatic conditions.

In use, the fog inhibitor "is dissolved in water at a convenient concentration .and added to 58 melted gelatino-tsilver halide photographic emul' sion in quantities ranging up to about 3.90 gins; per kilogram of silver nitrate converted to :silver halide. The "emulsion is coatedon a suitable support, glass, filmr'or other, and dried in a'normal fashion.

We also contemplate *asa part o1' our invention those cases where it is desirable to coat :thea ntifoggant inacolloid layer such assgelatin :on either or both sides of or also :in the :"silver halide emulsion layer :so that the anti-fogg'ant is in at least. one of the layers. In these'cases, we .1156 thesame' or a slightly greater ratio of rare metal :salt to silver halide than when the salt is in the 'emul-z sion layer.

The fog-inhibiting agents which we have dein ordinary non-sensitized emulsions they may also be used in onth'ochromatlc, panchromatic, and X-ray emulsions. It used with sensitizing dyes, they may be "added to the emulsion before or after the dyes are added. Various silver salts may be used as the sensitive salt, such as silver bromide, silver iodide, .silver chloride and mixtures of these. The dispersing agents may be gelatin or other colloid such as .collodion, albumen, cellulose derivatives, or synthetic resins.

It-will be understood that we contemplate as included within our invention an modifications and equivalents falling within "the scope of the appended claims.

What we-claim is:

1. A silver halide emulsion containing .palladium nitrate.

.2. A silver -halide emulsion layer containin from 0.26 to 3.9 grams of palladium nitrate per kilogram of silver nitrate used in making said emulsion and convertedto silver halide.

3. A.lighwsensitivephotographic element comprising =a -silver halide emulsion layer and a colloid layer contiguous to said silver halide emul sion layer, at least one of said layers containing palladium-nitrate.

ROBERT E. STAUFF-ER.

REFERENCES CITED The following re'feren ces -are of record in the file of this patent:

Number Schoenfelder et a1. slept. 29,1895 

